B 



\l i \. 



D 



Ol 





C 





1 



FIG. 49. Petromyzon. A. Extarnal view of entire animal from specimen; na, 

 median nasal aperture. B. Ventral view of head showing funnel-like oral sucker 

 armed with chitinous teeth; end of "tongue" in mouth opening. C. Dorsal 

 view of head, showing median nostril. D. Internal anatomy: 6s, branchial sac 

 cut open to show gill tissue; 6, brain; da, dorsal aorta; h, heart; N, notochord; 

 na, nasal aperture; leading into naso-pituitary sac (nps), ns, nasal sac; oe, cesoph- 

 agus quite independent of pharyngeal diverticulum (p}; of, oral funnel; sc, spinal 

 cord; tc, tongue cartilage. E. Ventral view of cranium: ac, auditory capsule; 

 oc, olfactory capsule. F. Dorsal view of cranium: N, notochord. G. Dorsal 

 view of brain: ch, cerebral hemispheres; cb, cerebellum; d, diencephalon; mo, 

 medulla oblongata; ol. olfactory lobe; opl, optic lobe; pn, pineal body. (Re- 

 drawn after Parker and Haswell.) 



93 



